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Inside the Machine G3 to G5 / Week 08 / Wednesday
3/6
Week 08 · Networks and the internet

Wednesday

Packets: a message in pieces
// How a message leaves the device and finds its way
⏱ about 15 min

Wednesday: Packets: a message in pieces

A neighbor sent a long video to her cousin, and it arrived with no problems. "How did such a huge file fit through one thin cable?" Rocket wonders.

Raven pulls a long paper banner from a drawer. "What do you notice? I cannot push this through the mail slot in one piece."

Nova hums. "Would you like a hint? Cut the banner into cards. Number the cards. Then send them one at a time."

Cut it into packets

A network does not send a message in one big piece. It cuts the message into small pieces called packets.

Each packet carries a little piece of the message. It might be a few words or a slice of a picture.

Each packet also carries a label. The label says who sent it and who it is for. It also has a number.

The numbers matter. Packets can arrive out of order. The number tells the receiver how to put them back.

PacketWho it is forNumberPiece of the message
1Cousin's tablet1 of 4Hello
2Cousin's tablet2 of 4from
3Cousin's tablet3 of 4Beacon
4Cousin's tablet4 of 4Station!

The receiving device waits for all four packets. Then it puts them in number order. The message reads: Hello from Beacon Station!

Look at the table. How many packets make up the whole message?
Which word is inside packet 3?
Packet 2 arrives last. Does the message still read correctly?
Packets arrive in this order: 3, 1, 4, 2. Which packet does the receiver read first when rebuilding?
WHY THIS EXERCISENumbering lets packets arrive in any order and still be rebuilt correctly.

Many paths, one message

The internet has many paths between any two places. Packets from one message can take different paths.

Some packets arrive early. Some arrive late. The numbers sort it out.

Sometimes a packet gets lost. The receiver notices a missing number and asks for that packet again.

This is why a huge video fits through a thin cable. It never goes through in one piece. It goes through in thousands of small packets.

Long message
↓
Cut into numbered packets
↓
Packets travel, maybe on different paths
↓
Receiver sorts them by number
↓
Message is rebuilt
PUT THE JOURNEY OF A MESSAGE IN ORDER.
  • ?The sending device cuts the message into packets
  • ?Packets travel across the network
  • ?The receiver sorts the packets by number
  • ?Each packet gets a label with address and number
  • ?The message is rebuilt and shown
WHY THIS EXERCISEEvery message on the internet follows these same steps, even a tiny one.
PACKET PUZZLES
  • Read the question.
  • Tap your answer.
A packet is missing. What does the receiving device do?
Why does each packet carry a number?
Can two packets from one message take different paths?
How does a huge video fit through a thin cable?
StatementTrue or false?
A message travels across the internet in one big piece.?
Each packet has an address and a number.?
Packets always arrive in the order they were sent.?
A lost packet can be sent again.?
WHY THIS EXERCISEPackets are the heart of how the internet works. These four facts describe them.
Try it
Write a short sentence on paper. Cut it into four pieces.
Number the pieces on the back. Shuffle them.
Hand them to a partner one at a time. Can they rebuild the sentence?

Nice work! You know a message travels as numbered packets. Tomorrow you will learn how each packet knows where to go.

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